1. Field of the Invention
The present invention relates to a nitrogen-containing Fe based soft magnetic alloy film suitable for use as the material of, for example, a core of a magnetic head.
2. Description of the Prior Art
Soft magnetic alloys used as the material of core of a magnetic head are required to have higher level of saturation magnetization to cope with recent demand for higher density of magnetic recording. On the other hand, in order to manufacture a practical magnetic head with a high reliability, it is important that a strong bonding with a bonding glass be made at the magnetic gap portion etc. of the magnetic head. In general, however, bonding glasses having high bonding strength exhibit a higher melting point. Soft magnetic alloy films, even if they exhibit high levels of saturation magnetization, are therefore required to exhibit good soft magnetic characteristics even after a heat treatment at a high temperature. Due to this restriction from the requirement concerning the thermal stability, conventional soft magnetic alloy films for magnetic heads used in VCR's, etc. have a practical upper limit of saturation magnetization on the order of 10 kGauss or so. In general, production of a soft magnetic alloy having superior soft magnetic characteristic essentially requires that the magnetic anisotropy and saturation magnetostriction constant .lambda.s be made as small as possible. Co-based amorphous alloy exhibits superior soft magnetic characteristics partly because of its magnetostriction constant .lambda.s being zero and partly because of its small magnetic anisotropy due to its amorphous state. Unfortunately, however, Co-based amorphous alloys generally exhibit lower saturation magnetization than Fe-base amorphous alloy represented by Fe-Si-B alloys. The use of the Co-based amorphous alloys also poses a problem from an economical point of view, because Co is considerably more expensive as compared with Fe. For these reasons, there has been a demand for ferrous soft magnetic alloys. The present inventors have discovered two types of Fe based magnetic alloys: namely, an Fe-Nb-B type alloy having magnetostriction constant .lambda.s of +1.times.10.sup.-5 and an Fe-Nb-Cu-B alloy having magnetostriction constant .lambda.s of +3.times.10.sup.-6, and proposed them in the specification of Japanese Patent Application No. 55-164978. These alloys exhibit improved wear resistance and corrosion resistance by virtue of addition of Nb but are rather inferior in thermal stability, wear resistance and corrosion resistance as compared with metal-metal amorphous alloys of Co-Nb-Zr type (see specifications of Japanese Patent Application Nos. 56-181723 and 56-212873) which are currently used as the material of VCR magnetic heads.
Nitriding is a measure which is available for improving wear resistance and corrosion resistance of the above-mentioned ferrous soft magnetic alloys. Studies such as a study on formation of nitride film through combination between Fe, Co, Ni and B, Si, Al, P, C etc. (see Japanese Patent Unexamined Publication No. 54-94428) and a study on Fe nitrides (see Journal of Applied Phys. Vol. 53 (11), pp 8332-34 (1982)) have been made in regard to nitriding of Fe based soft magnetic alloys. The technique disclosed in Japanese Patent Unexamined Publication No. 54-94428, however, encounters a problem in that the soft magnetic characteristic is seriously affected by an increase in the vertical magnetic anisotropy, and in that the level of the saturation magnetization is lowered. On the other hand, it has been reported that the technique disclosed in the Journal of Applied Phys. is disadvantageous in that the soft magnetic characteristic is impaired due to the fact that the coercive force of the alloy is increased as a result of nitriding of Fe.
As has been described, nitrides of alloys containing Fe as the major constituent possess wear resistance and corrosion resistance equivalent to those of Co-Nb-Zr alloys which are practically used, as well as higher level of saturation magnetization than Co-based alloys. In addition, these nitrides are rather inexpensive and, hence, are advantageous from the view point of economy. Unfortunately, however, these nitrides are not expected to exhibit superior soft magnetic characteristics.